Method of Producing Synthetic Pitch

ABSTRACT

Embodiments of a method are described for modifying pitches, oils, tars, and binders by using these materials as solvents to extract organic chemicals from coal.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional PatentApplication No. 60/808,084, filed May 24, 2006, the entire disclosure ofwhich is considered as part of the disclosure of the present applicationand is hereby incorporated by reference herein.

TECHNICAL FIELD

The present invention relates to synthetic pitch, particularly methodsfor producing synthetic pitch using solvent extraction of coal.

BACKGROUND

Pitches are hydrocarbon liquids that are solid at ambient temperature,but that melt upon heating. Upon further heating, volatile gases areevolved from the pitch, resulting in a solid residue that mainlycomprises carbon. This solid residue is referred to as coke. In general,pitches may comprise a wide range of chemicals with a distribution ofmolecular weights, rather than a single component.

Conventional pitches may be obtained as byproducts from petroleumrefining or metallurgical grade coke production ovens. In the lattercase, volatile components evolved during the coking process arecollected in the form of a tar. This tar may then be further refined byuse of distillation to remove low boiling point materials, resulting ina pitch residue. Both petroleum pitches and coal tar pitches can be usedfor a variety of applications including use as binder pitch, anode pitch(i.e., an anode coke precursor pitch), graphite pitch, impregnationpitch, hard pitch, soft pitch, and others.

Raw coal generally is not considered to be a pitch because itdevolatilizes before it can soften or melt. However, a synthetic pitch,also referred to as a “Synpitch,” can be created by extracting coal in ahydrocarbon solvent at an elevated temperature such that a molten slurryis formed. Typically, undissolved solids are removed by filtration orcentrifugation and the solvent is removed via distillation. Thesoftening point, coke yield, and aromatic content of the resultant pitchmay be modified by distillation and/or air blowing.

A related process is direct liquefaction, in which coal is converted toan oil similar to crude petroleum (see William F. Taylor and Homer J.Hall, Future Synthetic Fuels: A Scientific and Technical ApplicationsForecast—1975, US Army Contract DAA05-73-C-0559, Sep. 1975. See alsoIncreased Automobile Fuel Efficiency and Synthetic Fuels: Alternativesfor Reducing Oil Imports, NTIS order #PB83-126094, 1982). Directliquefaction involves the use of hydrogen to chemically bond withmolecules contained in coal, resulting in a more fluid material. Onemethod by which hydrogen is transferred to coal is through the use of anintermediate “donor solvent” that contains excess hydrogen that isavailable to be transferred to hydrogen-poor molecules in coal. Anexample of a hydrogen donor solvent is tetrahydronaphthalene (tetralin),which contains four excess hydrogen atoms in each molecule. Aftertransferring its excess hydrogen atoms to molecules contained in thecoal, the tetralin is converted to naphthalene. Naphthalene can bere-converted to tetralin by exposing it to high temperature and highpressure in the presence of a metal catalyst. Examples of high pressureand high temperatures are 2500 psi and 425° C., respectively (reference:Increased Automobile Fuel Efficiency and Synthetic Fuels: Alternativesfor Reducing Oil Imports, NTIS order #PB83-126094, 1982, p. 164. Seealso Baughman, Gary L., Synthetic Fuels Data Handbook. Second Edition,Denver, Colo.: Cameron Engineers, Inc. 1978).

The absorption of hydrogen by coal results in a more fluid material,especially at high temperature. By converting coal to a liquid in thismanner, it is possible to remove insoluble solids, such as, but notlimited to, fixed carbon and mineral matter, by either filtration orcentrifugation, resulting in a nearly pure hydrocarbon liquid.

The process of dissolving coal in a solvent and reconstituting itwithout insoluble solids present is generally known as solventextraction. It should be noted, however, that this is not a simplesolution process. Rather, because of the large number of chemicalspresent in coal, there are a variety of chemical processes that canresult in a phase change from solid to liquid. Specifically, it isthought that large molecular weight molecules contained in coal can bebroken down into smaller molecular weight molecules by hydrogen-richdonor solvents. True chemical reactions are also thought to be likely tooccur, as described above, such that hydrogen is physically transferredto certain molecules contained in coal. Thus, the solid-to-liquid phasechange of coal in the presence of a liquid donor solvent likely consistsnot only of dissolution but also chemical digestion. For that reason itis more accurate to say that coal is “extracted” by the liquid, ratherthan simply “dissolved,” although outwardly the process resemblesdissolution. Thus, as used herein, the term “extraction” (or “solventextraction”) means the removal of material from coal (or othersolids-containing mixture) by means of one or more solvents, wherein theremoved (i.e., “extracted”) material simply dissolves in the solvent(s)and/or reacts to form a compound that is soluble in the solvent(s).

Alternative solvent extraction techniques for producing synthetic pitchfrom coal have been described previously. For example, Zondlo et al(U.S. Pat. No. 5,955,375, which is incorporated herein by reference)describe a solvent extraction process for coal using an NMP-typesolvent. These solvents are described, for example, in U.S. Pat. No.4,272,356 (hereinafter, “Stiller et al.”), which is also incorporatedherein by way of reference. In the process described by Zondlo et al.,the solvent is separated from the final product via evaporation or someother process. In typical solvent extraction processes for producingsynthetic pitch from coal, the final product contains about 2% or less(by weight) of components derived from the solvent. In other words, atleast 98% of the solvent is recovered and typically is recycled back tothe extraction process. Because of the expense of the solvents typicallyused for producing synthetic pitch from coal, the process generally isnot economical if more than a few percent of the solvent is left in thefinal product. In addition, the desired properties of the syntheticpitch may be adversely affected if too much solvent remains in the finalproduct.

Blending is a well-known method to modify pitch properties. For example,Stansberry et al. describe how synthetic pitch may be blended withconventional coal tar pitch and other hydrocarbons in order to createmodified pitches having certain desirable properties. Stansberry, P. G.,J. W. Zondlo, and R. H. Wombles; Development of binder pitches from coalextract and coal-tar pitch blends; Light Metals, 581-585 (2001).However, the use of blended hydrocarbons as a solvent for extractingcoal has not been previously described.

SUMMARY

One embodiment provides a method of producing a synthetic pitch fromcoal, comprising:

(a) heating an extraction mixture comprising solid hydrocarbons and atleast one feedstock solvent for a period of time sufficient to extractone or more soluble portions of the solid hydrocarbons in the at leastone feedstock solvent;

(b) removing undissolved solids from the extraction mixture; and

(c) removing at least a portion of low-boiling point species from theextraction mixture, thereby producing a synthetic pitch, wherein betweenabout 10% and about 90% by weight of the pitch comprises speciesprovided by the at least one feedstock solvent.

In one embodiment, between about 10% and about 15% by weight of thepitch comprises species provided by the at least one feedstock solvent.A variety of solid hydrocarbons may be used in the process, particularlycoal. At least a portion of the at least one feedstock solvent may alsobe hydrogenated prior to being heated with the solid hydrocarbons.Hydrogenation may be performed by heating at least a portion of thefeedstock solvent to a temperature of between about 200° C. and about500° C. in a hydrogen atmosphere with a hydrogen pressure of up to about3000 psig, such that the feedstock solvent of the extraction mixture hasbetween about 0.1% and about 10% absorbed hydrogen by weight.

A variety of feedstock solvents may be used, such as coal tardistillates, petroleum distillates, petroleum catalytic crackerproducts, distillates of gasification tars, products from the pyrolysisof recycled hydrocarbons, and aromatic oil products obtained from thedistillation of shale oil and tar sands. By way of example, thefeedstock solvent may comprise a hydrocarbon material having a softeningtemperature less than about 200° C., and contain at least 10% by weightof hydrocarbon species having a boiling point greater than about 350° C.

The method of the present invention may further include the step of airblowing the extraction mixture at a temperature of between about 70° C.and about 500° C. after the step of removing at least a portion oflow-boiling point specie. In addition, the extraction mixture may beagitated during heating, wherein the agitating step is performed by atleast one of mechanical stirring and applying ultrasound.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a chart depicting an example of coal conversion using varioussolvents in accordance with one embodiment;

FIG. 2 is a chart depicting an example of the benefits of hydrogenationof the feedstock solvent on coal conversion, in accordance with oneembodiment;

FIG. 3 is a photomicrograph of an example of a synthetic pitch producedin accordance with one embodiment; and

FIG. 4 is a block flow diagram of an example of a processing system thatmay be used to produce synthetic pitch in accordance with oneembodiment.

DETAILED DESCRIPTION

In one embodiment, the present invention provides a process forproducing synthetic pitch from a mixture of solid hydrocarbons, such ascoal, using solvent extraction, wherein at least part of the solvent(s)used for extraction remains in the synthetic pitch product. At least aportion of the extraction solvent(s) may be hydrogenated, andhydrogenation may be performed prior to solvent extraction. A portion ofthe coal (or other mixture of solid hydrocarbons) is extracted using oneor more feedstock solvents (the extraction solvents). Thereafter,undissolved solids may be removed (e.g., using centrifugation and/orfiltration). In the case of coal, the result is a hydrocarbon liquidcontaining solvent and the extracted coal components, with less thanabout 1% mineral matter content. This hydrocarbon liquid may be furtherrefined by processes such as distillation or air blowing. For example,light hydrocarbons and a portion of the feedstock solvent(s) may beremoved and recycled for subsequent re-use in the process. Air blowingmay be accomplished by exposing the hydrocarbon liquid to air, typicallyby bubbling or blowing air through the liquid. Air blowing cross-linkscertain molecules within the hydrocarbon liquid or to otherwise entrainor remove organic molecules in the vapor state.

The resulting synthetic pitch product thus may be comprised of not onlymaterial extracted from the coal (or other mixture of solidhydrocarbons), but also contains between about 10% and about 90% (byweight) of materials derived from the solvent(s) used for extraction. Inanother embodiment, the resulting synthetic pitch contains between about10% and about 15% (by weight) of materials derived from the solvent(s)used for extraction. In addition, hydrogenation of the feedstocksolvent(s) may improve the extractability of coal, thus allowing the useof lower cost solvents either in combination with solvents such astetralin or in place of tetralin.

In some embodiments, two or more feedstock solvents may be blendedtogether in order to tailor the properties of the synthetic pitchproduct. By way of example, for binder and impregnating pitchapplications, the table (Table 1) below provides exemplary binder pitchproperties that may be achieved with embodiments of the methodsdescribed herein:

TABLE 1 Binder Pitch Impregnating Pitch Softening Pt 100-120° C. 75-150°C. Viscosity <20 poise @ 160° C. <50 cps @ 225° C. Flash Pt ≧200° C.≧270° C. Coking Value 50-60 40-50 (wt %)

In order to further improve the solvent extraction (i.e., improve coalsolubility) and tailor the properties of the synthetic pitch product, atleast a portion of the feedstock solvent(s) may be hydrogenatedexternally prior to being mixed with the unhydrogenated portion of thefeedstock solvent(s). While all of the feedstock solvent(s) may behydrogenated, this is usually not necessary (and adds to processingcosts). The hydrogenated solvent(s) or blend of hydrogenated solventsare found to be effective in incorporating coal to a liquid phasethrough a process that resembles simple dissolution. However, it isthought that molecules in coal may be incorporated into the liquid phasethrough one of three routes. First, coal molecules may be dissolved inthe solvent. Second, the coal may be broken down into, lower molecularweight species. These lower molecular weight species may be more readilydissolved or incorporated into the liquid phase solution. Third,hydrogen may be physically transferred from the solvent molecules tochemicals contained in the coal, modifying their solubilitycharacteristics. Thus, in addition to simple dissolution, the presenceof hydrogen may result in digestion and breakdown of polymeric coalmolecules, thus resulting in smaller chemical species that can beincorporated into a liquid phase. In fact, Applicants have found thatblends of solvents containing both hydrogenated and non-hydrogenatedcomponents can improve the yield to over 90%, particularly when theextraction is performed at an elevated temperature. Furthermore, one ormore inorganic catalysts may be added in order to increase the yield ofcoal extraction.

Although not required, it is also contemplated that one or moreadditional solvents, such as, but not limited to, tetralin, decalin,tetrahydrofuran, or aprotic dipolar solvents, such as, but not limitedto, n-methyl pyrrolidone (“NMP”) may be blended with the feedstocksolvent(s) in order to decrease the viscosity of the resultant solutionand to enhance the solubility of coal in the solution. By reducing theviscosity of the solution, processing will be facilitated (particularlyremoval of the undissolved solids, such as, by use of centrifugation).When an additional solvent is employed, most of the additional solventwill be removed from the final pitch product and recycled back into theprocess.

Furthermore, in some embodiments, the synthetic pitch product may bedistilled in order to remove low boiling point light volatile chemicals,and then air blown in order to crosslink hydrocarbon molecules withoutoxidation, resulting in a modification of the softening point andincreased coke yield. Air blowing may also reduce the amount of lowboiling point species that much be removed from the product. Air blowingparameters may even be controlled in order to tailor the properties ofthe synthetic pitch product.

FIG. 4 is a block flow diagram depicting an exemplary processing systemthat may be used to produce synthetic pitch in accordance with one ormore embodiments. While FIG. 4 is merely exemplary, the followingdetailed description of methods of producing synthetic pitch accordingto one or more embodiments, at times, refer to FIG. 4 for purposes ofclarity.

As shown in FIG. 4, all or a portion of the feedstock solvent(s) usedfor coal extraction may be fed to a high pressure heated tank reactor(or other suitable vessel) along with hydrogen gas in order tohydrogenate a portion of the feedstock solvent(s). Optionally, acatalyst, such as, but not limited to, iron, cobalt, nickel, molybdenum,tin, salts of the foregoing metals, or mixtures of any of the foregoing,may also be added to the reactor in order to enhance the absorption ofhydrogen by the solvent. The feedstock solvent(s) may be hydrogenatedsuch that the feedstock solvent mass may be increased by up to severalpercent due to absorption of hydrogen. Following hydrogenation of atleast a portion of the feedstock solvent(s), the hydrogenated solvent(s)may be combined with one or more unhydrogenated feedstock solvents, and,optionally, one or more additional solvents (e.g., tetralin). Theblended solvent thus produced may have about 0.1% to about 10% (byweight) absorbed hydrogen, or between about 0.2% to about 5% absorbedhydrogen. As also noted in FIG. 4, and as described further herein,solvent that has been removed from the pitch product may be blended withthe feedstock solvent(s) prior to being added to a second tank reactorin which the extraction takes place. This solvent recycle stream mayinclude not only solvent (feedstock and additional solvent) and solventfractions removed from the pitch, but also other light hydrocarbonsextracted from the coal. As used herein, “light hydrocarbons” refer tomaterials having a boiling point lower than about 200° C., making themdifficult to incorporate into a pitch product intended to withstanddevolatilization until over 350° C. Recycling of a portion of thesolvent can permit dissolution of additional quantities of coal.Alternatively, the portion of solvent removed from the final pitchproduct may be considered a separate product (e.g., for use as an octaneenhancer).

After hydrogenation, the feedstock solvent(s) and optional additionalsolvent(s) and recycled solvent(s) may be transferred to a second heatedreactor and combined with coal (or other solids-containing material tobe extracted). In one embodiment, the mass ratio of coal to totalsolvents may be about 1:2.5 or greater. The solvent(s) will extract thecoal in the manner described previously. The second heated reactor maybe operated at ambient pressure, since hydrogen gas is not necessary.While the feedstock solvent(s) and coal may be hydrogenatedsimultaneously in the extraction vessel, hydrogenating the feedstocksolvent(s) in a separate reactor before extraction avoids the need todeal with solid particulates from the coal in a high pressure, hightemperature reactor. It is also possible to avoid the hydrogenation stepcompletely, however, in this case, the solubility of coal in thesolvents is decreased.

In some embodiments, any of a variety of coals may be used as a feedmaterial for making synthetic pitch. However, Applicants have found thatbituminous, sub-bituminous, and lignite type coals may be suitable forthe production of binder pitch. In one embodiment, the coal may bereduced in physical size to particles of less than about ¼ diameter. Infact, the coal may be in the form of a powder (e.g., particles less thanabout 20 mesh, or less than about 1 mm in diameter). The coal may beplaced, for example, in a bin feeder or other container and fed by anauger or other solid feeding system into the second tank reactor (seeFIG. 4).

As mentioned previously, a wide variety of hydrocarbon feedstocksolvents may be used in some embodiments, particularly those which areproduced in large quantities, such as oils distilled from coal tars orpetroleum (i.e., coal tar distillates and petroleum distillates). Thefeedstock solvent(s) not only extracts the coal, but also contributesvarious hydrocarbon molecules that are incorporated into the syntheticpitch product of one or more embodiments of the present invention. Inparticular, hydrocarbon materials containing at least about 10% byweight of hydrocarbon species having a boiling point greater than about350° C. and that have a softening temperature less than about 200° C.may be used. A high boiling point is desirable because hydrogenation isgenerally not very effective below about 350° C. The feedstocksolvent(s) may also be a liquid at a temperature of about 200° C. andhigher so that coal may be extracted into the liquid phase, while theinsoluble material from coal can be separated from the liquid phase.

Exemplary feedstock solvents that may be employed in some embodimentsinclude:

-   A. Distillates of coal tar.

Coal tar may be produced by condensing vapors from coal coking ovens andcertain coal gasifiers. By convention, the distillates of coal tar areoften broken into three major groups: light distillates, mediumdistillates, and heavy distillates. The light distillates typically aredistilled below about 200° C. and contain compounds such as benzene,toluene, xylene, phenol and others. Middle distillates, obtained atroughly 200° C. to 300° C., are sometimes referred to as naphthaleneoils, middle oils, creosote oils, wash oils, anthracene oils and heavyoils, for example. Middle distillates of coal tar often containcompounds such as: naphthalene; indene; biphenyl heterocyclic compoundssuch as quinoline, pyridine and/or phenol; various combinations of twoaromatic rings and single alkyl groups such as acenaphthene,dibenzofurane and methyl fluorenes. The heavy distillates of coal tarare obtained from about 300° C. to 350° C., and include anthracene oiland/or heavy oil, which contain compounds having three or four aromaticring structures such as anthracene, fluoranthene, pyrene, crysene andsystems of hetero-atoms like carbazol.

-   B. Petroleum derived liquids.

Various liquids derived from petroleum, including, but not limited to,distillation products (i.e., petroleum distillates) as well as petroleumcatalytic cracker products, may also be used as feedstock solvents.These include substances such as, but not limited to, naphthalene,decant oil slurry oil and other heavy aromatic oils capable of acceptingand transferring hydrogen.

-   C. Distillates of gasifications tars, such as, but not limited to,    those obtained as condensates from gasified coal, gasified biomass,    gasified polymer waste or other gasified carbonaceous material. In    addition, products synthesized from gasified coal, gasified biomass,    gasified polymer waste or other gasified carbonaceous material may    be used as feedstock solvent(s). These products include, for    example, products made by Fischer-Tropsch synthesis using the    aforementioned gasified materials.-   D. Products obtained from the pyrolysis of recycled hydrocarbons,    such as, but not limited to, used motor oil, rubbers (e.g., recycled    tire rubber), and thermoplastics (e.g., polypropylene, polyester or    polyvinyl chloride), thermosets, grease, and chemical wastes.-   E. Aromatic oil products obtained from the distillation shale oil or    tar sands.

It has been found that coal solubility and coke yield of the pitchproduct may be improved if a portion of the feedstock solvent(s) ishydrogenated, such as when hydrogenation is performed prior to blendingwith other solvents and before the solvent blend is combined with thecoal. Hydrogenation may be accomplished by a variety of techniques, suchas by exposing the feedstock solvent to hydrogen gas at an elevatedtemperature and H₂ pressure, optionally in the presence of a metalliccatalyst. For most feedstock solvents, hydrogenation can be accomplishedat a temperature of between about 200 and about 500° C. (e.g., betweenabout 350 and about 500° C.), and an H₂ pressure of up to about 3000psig (e.g., greater than about 400 psig). In this manner, the hydrogencontent of the hydrogenated solvent will be increased by at least about0.1% (by weight), thus effecting a partial direct liquefaction of thehydrocarbons in the feedstock solvent and increasing the aromaticcontent. Typically between about 25% and about 100% of the feedstocksolvent may be hydrogenated.

One or more inorganic catalysts may also be added to the tank reactor tofacilitate hydrogenation of the feedstock solvent, thus resulting in anincreased amount of hydrogen absorption. Suitable catalysts include, butare not limited to, various pure metals or salts of iron, cobalt,nickel, molybdenum or tin, or mixtures thereof. Suitable catalysts caninclude a mixture of 3% nickel, 13% molybdenum, and 84% aluminum. Othercombinations of nickel and molybdenum on various supports may also beused as a catalyst. The catalyst(s) is not consumed during the process,so, for example, a kilogram of catalyst can be used to process many tonsof solvent. These catalysts, when added to the hydrogen reactor (thefirst tank reactor in FIG. 4) may increase the amount of hydrogen thatcan be absorbed by the solvent and ultimately transferred to the coal.Also, the use of one or more catalysts may lower the temperature neededfor extraction.

In the extraction vessel (e.g., the second tank reactor in FIG. 4), thecrushed coal may be mixed with a solvent or solvent blend (e.g., one ormore feedstock solvents and one or more additional solvents) at atemperature greater than about 100° C. such that the solvent(s) canextract the coal. In one embodiment, the extraction mixture may beheated until the coal begins to decompose thermally, typically betweenabout 350° C. and about 425° C. In order to improve extraction, theextraction mixture may be agitated, such as by mechanical stirringand/or by use of ultrasound. The result is a slurry of undissolvedsolids in a hydrocarbon liquid solution comprising the solvent(s) anddissolved (i.e., extracted) coal. In one embodiment, at least about 85%of the coal is extracted into the solvent(s). The solvent extractionneed not be performed under a hydrogen atmosphere, however, a hydrogenatmosphere may optionally be used in order to enhance the absorption ofhydrogen.

After completion of the extraction process, the undissolved solids inthe slurry may be removed, such as by filtration or centrifugation,thereby leaving a liquid phase solution containing the extracted coalcomponents and the solvent(s). Following extraction, additional solventmay optionally be added in order to reduce the viscosity of the slurry,thus enhancing the effectiveness of centrifugation or filtration. By wayof example, the slurry may be pumped (e.g., via a sludge pump) from theextraction vessel to a centrifuge. The centrifuge can separate liquidphase material from undissolved solids. The undissolved solids maysimply be deposited into a bin or other storage device. Theseundissolved solids will typically include solid mineral matter, such asinertinite and charcoal. The undissolved solids may be added to asphaltas a filler, used as combustion fuel, or gasified to produce a processgas and hydrogen.

After removal of undissolved solids, the remaining extraction mixturemay comprise hydrocarbon liquids and soluble, coal-derived species. Thissolution may then flow to a solvent separation unit, such as any of avariety of fractional distillation units, such as, but not limited to, awiped film evaporator or distillation column. In the solvent separationunit, the extraction mixture may be distilled in order to removelow-boiling point species, including excess solvent (particularly anyadditional solvents employed). A purified, synthetic pitch may becollected (e.g., in a collection drum). This pitch may have enhancedaromaticity, increased softening point, increased cross-linkingreactivity, and increased carbon coking value compared to the pitchproperties prior to distillation. Upon cooling to a temperature belowabout 110° C., the resultant synthetic pitch generally solidifies.

The pitch thus produced can have properties making it suitable for useas a binder pitch. Binder pitch may be used either for carbon anodes forHall Heroult cells for aluminum smelting, for graphite electrodes forelectric arc furnaces, or for other purposes. The pitch produced inaccordance with the embodiments may also be used for other purposes,such as, but not limited to, an impregnation pitch used to producecarbon composites, as well as fiber spinning pitch used to producecarbon fibers. The low-boiling point species removed in the solventseparation unit may be optionally recycled back to be blended with thesolvents used for subsequent coal extraction, with or without anadditional hydrogenation cycle.

After distillation to separate lighter fractions as described above, airblowing can optionally be used to crosslink heavier molecules in thepitch, thus increasing the average molecular weight of the pitch productand creating a potential precursor for anode-grade coke (i.e., slightlyanisotropic) or needle coke (more highly anisotropic). If air blowing isperformed prior to removing lighter fractions from the product, theresultant pitch may produce a more isotropic coke that may not besuitable for anode grade coke or needle coke. Air blowing of theextraction mixture may be performed at a temperature of between about250° C. and about 450° C. This can be accomplished, for example, bybubbling air through a tube inserted in a tank containing the pitch.Alternatively, a sparger can be used to increase mixing between air andpitch.

The following examples are meant to illustrate exemplary embodiments ofthe present invention, and are not intended to limit the scope of theembodiments as described herein and as defined in the claims:

1. Use of Solvent Blends to Enhance Coal Extraction

Experiments were carried out with different solvents to determinewhether hydrogenation improved the apparent solubility of coal in eachsolvent. Solvents trialed included carbon black base oil (“CBB”, a coaltar distillate obtained from Koppers), anthracene oil (“AO”, a coal tardistillate obtained from Reilly Industries), Maraflex® Oil (“MO”, amixture of petroleum distillates obtained from Marathon-Ashland),residual catalytic cracker slurry oil (“SO”, obtained fromMarathon-Ashland), and tetrahydronaphthalene (“tetralin”).

FIG. 1 depicts the coal conversion, in mass percent, obtained usingbituminous coal and the above-mentioned solvents. The crushed coal wasplaced into a sealed container along with the identified solvent at 400°C. for approximately one hour. Pressure within the sealed container wascontrolled by the vapor pressure of the solvent used. The coalconversion reported in the figure below is simply the fraction of coalmass that was converted from a solid to a liquid phase. These resultsindicate that tetralin, a know hydrogen donor solvent, is better thanthe other solvents in terms of coal conversion.

In order to determine whether hydrogenation can enhance the ability toextract coal in the liquid phase, three different hydrogenationconditions were established, as shown in Table 2.

TABLE 2 Solvent Hydrogenation Results Wt % H2 Hydrogenation Initial coldH2 Run Description absorbed Reactor T, ° C. Pressure (psig) CBBHydrogenation 0.10 275 500 Level 1 CBB Hydrogenation 0.14 350 500 Level2 CBB Hydrogenation 0.24 375 750 Level 3 Slurry Oil 0.24 375 750Hydrogenation Level 3 Maraflex Oil 0.24 375 750 Hydrogenation Level 3

Coal extraction using these hydrogenated solvents was performed in thesame manner as described previously. As shown in FIG. 2, coal conversionusing hydrogenated solvents from coal tar distillates (e.g., carbonblack base oil) is significantly improved as compared to the use ofnon-hydrogenated forms of those same solvents. In fact, the performancewas similar to that of tetralin.

Subsequently, experiments with bituminous coal and CBB L3 produced coalconversion of 90% at 425° C. This shows that hydrogenation ofhydrocarbon materials can produce an effective alternative to tetralin,a much more expensive solvent that generally cannot be economicallyincorporated into the pitch product.

2. Distilling Coal Extract to Form Pitch of Desired Softening Point &Coke Yield

After removing the insoluble solids from the liquid phase extract (e.g.,by centrifugation), it generally is necessary to distill the liquidphase extract so that lower boiling point volatile molecules areremoved, and the softening point of the extract is raised. Bycontrolling the distillation temperature, the characteristics of theextract can likewise be controlled, especially its softening point.Generally, removal of lower boiling point liquids results in elevatingthe softening point of the mixture.

Optionally, air blowing can be used to complement distillation. Airblowing involves heating the extract and exposing the extract to air,usually with the aid of a sparger that blows air in from the bottom ofthe extract container. The effect of air blowing is to encouragecross-linking of molecules in the extract. If air blowing isaccomplished without removing lower molecular weight, lower boilingpoint volatile molecular species, the result is an extract with a moreisotropic character. Thus, if such an extract is further heated in anoxygen-depleted environment, the resultant coke is very isotropic.Conversely, by removing low molecular weight volatile species viadistillation at a temperature in excess of 100° C., followed byair-blowing at a temperature in excess of 200° C., a more anisotropiccoke precursor can be formed. That is, when the air-blown extract isfurther heated in an oxygen-depleted environment to create coke, a moreanisotropic coke is formed.

FIG. 1 illustrates a 160× polarized light photomicrograph of oneembodiment of a synthetic pitch distilled and then treated by airblowing. The resultant material is anisotropic as evidenced by thecontoured regions visible under polarized light.

The specific illustrations and embodiments described herein areexemplary only in nature and are not intended to be limiting of theinvention defined by the claims. Further embodiments and examples willbe apparent to one of ordinary skill in the art in view of thisspecification and are within the scope of the claimed invention.

1. A method of producing a synthetic binder pitch from coal, comprising: (a) hydrogenating feedstock solvent in a first tank reactor, wherein the feedstock solvent comprises at least one additional solvent selected from the group consisting of: tetralin, decalin, tetrahydrofuran, and aprotic dipolar solvents such as n-methyl pyrrolidone; (b) producing a mixture of hydrogenated and unhydrogenated feedstock solvents by combining said hydrogenated feedstock solvent exiting said first tank reactor with unhydrogenated feedstock solvent; (c) combining said mixture of hydrogenated and unhydrogenated feedstock solvents with coal to produce an extraction mixture in a second tank reactor downstream of said first reactor; (d) heating said extraction mixture for a period of time sufficient to extract one or more soluble portions of said coal into said mixture of hydrogenated and unhydrogenated feedstock solvents; (e) removing undissolved solids from said extraction mixture; (f) removing light hydrocarbons from said extraction mixture, thereby producing a the synthetic binder pitch, wherein the synthetic binder pitch comprises a softening temperature between 100 and 120° C. and a coking value between 50 and 60% by weight; and (g) recycling said light hydrocarbons and at least a portion of said mixture of hydrogenated and unhydrogenated feedstock solvents to said second tank reactor.
 2. The method of claim 1, wherein between about 10% and about 15% by weight of said pitch comprises species provided by said at least one feedstock solvent 3-4. (canceled)
 5. The method of claim 1, wherein said at least one feedstock solvent is selected from the group consisting of coal tar distillates, petroleum distillates, petroleum catalytic cracker products, distillates of gasification tars, products from the pyrolysis of recycled hydrocarbons, and aromatic oil products obtained from the distillation of shale oil or tar sands.
 6. The method of claim 1, wherein said hydrogenating step comprises heating at least a portion of the feedstock solvent to a temperature of between about 200° C. and about 500° C. in a hydrogen atmosphere with a hydrogen pressure of up to about 3000 psig, such that the feedstock solvent of the extraction mixture has between about 0.1% and about 10% absorbed hydrogen by weight.
 7. (canceled)
 8. The method of claim 1, wherein at least 10% of said feedstock solvent comprises one or more of coal tar distillates, petroleum distillates, or distillates of gasification tars. 9-16. (canceled)
 17. The method of claim 1, further comprising the step of air blowing said extraction mixture at a temperature of between about 70° C. and about 500° C. after said step of removing at least a portion of said light hydrocarbons.
 18. The method of claim 1, further comprising the step of agitating said extraction mixture during heating, wherein said agitating step is performed by at least one of mechanical stirring and applying ultrasound.
 19. The method of claim 1, further comprising the step of agitating said feedstock solvent in the presence of hydrogen, in order to enhance absorption of hydrogen, wherein such agitating step is performed by at least one of mechanical stirring and applying ultrasound.
 20. The method of claim 1, wherein said coal is selected from the group consisting of bituminous coals, sub-bituminous coals, and lignite coals.
 21. The method of claim 1, wherein at least 85% of said coal is extracted by said mixture of hydrogenated and unhydrogenated feedstock solvents.
 22. A method of producing a synthetic binder pitch from coal, comprising: (a) hydrogenating feedstock solvent in a first tank reactor, wherein the feedstock solvent comprises at least one additional solvent selected from the group consisting of: tetralin, decalin, tetrahydrofuran, and aprotic dipolar solvents such as n-methyl pyrrolidone; (b) producing a mixture of hydrogenated and unhydrogenated feedstock solvents by combining said hydrogenated feedstock solvent exiting said first tank reactor with unhydrogenated feedstock solvent; (c) combining said mixture of hydrogenated and unhydrogenated feedstock solvents with coal to produce an extraction mixture in a second tank reactor downstream of said first reactor, wherein said coal is selected from the group consisting of bituminous coals, sub-bituminous coals, and lignite coals; (d) heating said extraction mixture for a period of time sufficient to extract one or more soluble portions of said coal into said mixture of hydrogenated and unhydrogenated feedstock solvents, wherein at least 85% of said coal is extracted into said mixture of hydrogenated and unhydrogenated feedstock solvents; (e) removing undissolved solids from said extraction mixture by centrifugation; (f) removing light hydrocarbons from said extraction mixture in a fractional distillation unit, thereby producing the synthetic binder pitch, wherein the synthetic binder pitch comprises a softening temperature between 100 and 120° C. and a coking value between 50 and 60% by weight; and (g) recycling said light hydrocarbons and at least a portion of said mixture of hydrogenated and unhydrogenated feedstock solvents to said second tank reactor. 